Missing endbr64 instruction for x64

[mlgiraud]

As the title says it seems like the x64 assembler is missing support to encode the endbr64 instruction. Have i overlooked this or is it simply not supported at the moment? If it is not supported, i can contribute a PR if you point me in the right direction.

[CensoredUsername]

Hey,

You're correct, that instruction is currently not supported. This isn't intentional, it looks like that instruction is part of an extension that was only defined after most of the x64 backend was created.

It should be fairly simple to add, the encoding is 0F 1E FA with a forced REP prefix. so you can add the following in src/plugin/arch/x64/gen_opmap.rs:

"endbr64" = [
    b""           , [0x0F, 0x1E, 0xFA], X, PREF_F3, extension_set;
]

where extension_set is the relevant new feature set to be classified under (see https://github.com/CensoredUsername/dynasm-rs/blob/master/plugin/src/arch/x64/x64data.rs#L82-L109)